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| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Termination</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="support.html" title="Chapter 4. Support" /><link rel="prev" href="dynamic_memory.html" title="Dynamic Memory" /><link rel="next" href="diagnostics.html" title="Chapter 5. Diagnostics" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Termination</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><th width="60%" align="center">Chapter 4. |
| Support |
| |
| </th><td width="20%" align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="std.support.termination"></a>Termination</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.handlers"></a>Termination Handlers</h3></div></div></div><p> |
| Not many changes here to <code class="filename">cstdlib</code>. You should note that the |
| <code class="function">abort()</code> function does not call the |
| destructors of automatic nor static objects, so if you're |
| depending on those to do cleanup, it isn't going to happen. |
| (The functions registered with <code class="function">atexit()</code> |
| don't get called either, so you can forget about that |
| possibility, too.) |
| </p><p> |
| The good old <code class="function">exit()</code> function can be a bit |
| funky, too, until you look closer. Basically, three points to |
| remember are: |
| </p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p> |
| Static objects are destroyed in reverse order of their creation. |
| </p></li><li class="listitem"><p> |
| Functions registered with <code class="function">atexit()</code> are called in |
| reverse order of registration, once per registration call. |
| (This isn't actually new.) |
| </p></li><li class="listitem"><p> |
| The previous two actions are <span class="quote">“<span class="quote">interleaved,</span>”</span> that is, |
| given this pseudocode: |
| </p><pre class="programlisting"> |
| extern "C or C++" void f1 (void); |
| extern "C or C++" void f2 (void); |
| |
| static Thing obj1; |
| atexit(f1); |
| static Thing obj2; |
| atexit(f2); |
| </pre><p> |
| then at a call of <code class="function">exit()</code>, |
| <code class="varname">f2</code> will be called, then |
| <code class="varname">obj2</code> will be destroyed, then |
| <code class="varname">f1</code> will be called, and finally |
| <code class="varname">obj1</code> will be destroyed. If |
| <code class="varname">f1</code> or <code class="varname">f2</code> allow an |
| exception to propagate out of them, Bad Things happen. |
| </p></li></ol></div><p> |
| Note also that <code class="function">atexit()</code> is only required to store 32 |
| functions, and the compiler/library might already be using some of |
| those slots. If you think you may run out, we recommend using |
| the <code class="function">xatexit</code>/<code class="function">xexit</code> combination from <code class="literal">libiberty</code>, which has no such limit. |
| </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="support.termination.verbose"></a>Verbose Terminate Handler</h3></div></div></div><p> |
| If you are having difficulty with uncaught exceptions and want a |
| little bit of help debugging the causes of the core dumps, you can |
| make use of a GNU extension, the verbose terminate handler. |
| </p><pre class="programlisting"> |
| #include <exception> |
| |
| int main() |
| { |
| std::set_terminate(__gnu_cxx::__verbose_terminate_handler); |
| ... |
| |
| throw <em class="replaceable"><code>anything</code></em>; |
| } |
| </pre><p> |
| The <code class="function">__verbose_terminate_handler</code> function |
| obtains the name of the current exception, attempts to demangle |
| it, and prints it to stderr. If the exception is derived from |
| <code class="classname">exception</code> then the output from |
| <code class="function">what()</code> will be included. |
| </p><p> |
| Any replacement termination function is required to kill the |
| program without returning; this one calls abort. |
| </p><p> |
| For example: |
| </p><pre class="programlisting"> |
| #include <exception> |
| #include <stdexcept> |
| |
| struct argument_error : public std::runtime_error |
| { |
| argument_error(const std::string& s): std::runtime_error(s) { } |
| }; |
| |
| int main(int argc) |
| { |
| std::set_terminate(__gnu_cxx::__verbose_terminate_handler); |
| if (argc > 5) |
| throw argument_error("argc is greater than 5!"); |
| else |
| throw argc; |
| } |
| </pre><p> |
| With the verbose terminate handler active, this gives: |
| </p><pre class="screen"> |
| <code class="computeroutput"> |
| % ./a.out |
| terminate called after throwing a `int' |
| Aborted |
| % ./a.out f f f f f f f f f f f |
| terminate called after throwing an instance of `argument_error' |
| what(): argc is greater than 5! |
| Aborted |
| </code> |
| </pre><p> |
| The 'Aborted' line comes from the call to |
| <code class="function">abort()</code>, of course. |
| </p><p> |
| This is the default termination handler; nothing need be done to |
| use it. To go back to the previous <span class="quote">“<span class="quote">silent death</span>”</span> |
| method, simply include <code class="filename">exception</code> and |
| <code class="filename">cstdlib</code>, and call |
| </p><pre class="programlisting"> |
| std::set_terminate(std::abort); |
| </pre><p> |
| After this, all calls to <code class="function">terminate</code> will use |
| <code class="function">abort</code> as the terminate handler. |
| </p><p> |
| Note: the verbose terminate handler will attempt to write to |
| stderr. If your application closes stderr or redirects it to an |
| inappropriate location, |
| <code class="function">__verbose_terminate_handler</code> will behave in |
| an unspecified manner. |
| </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="dynamic_memory.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="support.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="diagnostics.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Dynamic Memory </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 5. |
| Diagnostics |
| |
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